Cafolla Clodomiro, Voïtchovsky Kislon
Physics Department, Durham University, Durham, DH1 3LE, UK.
Sci Rep. 2021 Oct 1;11(1):19540. doi: 10.1038/s41598-021-98137-y.
The behaviour of ions at solid-liquid interfaces underpins countless phenomena, from the conduction of nervous impulses to charge transfer in solar cells. In most cases, ions do not operate as isolated entities, but in conjunction with neighbouring ions and the surrounding solution. In aqueous solutions, recent studies suggest the existence of group dynamics through water-mediated clusters but results allowing direct tracking of ionic domains with atomic precision are scarce. Here, we use high-speed atomic force microscopy to track the evolution of Rb, K, Na and Ca nano-domains containing 20 to 120 ions adsorbed at the surface of mica in aqueous solution. The interface is exposed to a shear flow able to influence the lateral motion of single ions and clusters. The results show that, when in groups, metal ions tend to move with a relatively slow dynamics, as can be expected from a correlated group motion, with an average residence timescale of ~ 1-2 s for individual ions at a given atomic site. The average group velocity of the clusters depends on the ions' charge density and can be explained by the ion's hydration state. The lateral shear flow of the fluid is insufficient to desorb ions, but indirectly influences the diffusion dynamics by acting on ions in close vicinity to the surface. The results provide insights into the dynamics of ion clusters when adsorbed onto an immersed solid under shear flow.
离子在固液界面的行为支撑着无数现象，从神经冲动的传导到太阳能电池中的电荷转移。在大多数情况下，离子并非孤立存在，而是与相邻离子及周围溶液共同作用。在水溶液中，近期研究表明通过水介导的簇存在基团动力学，但能够以原子精度直接追踪离子域的结果却很少。在此，我们使用高速原子力显微镜来追踪含有20至120个离子的Rb、K、Na和Ca纳米域在水溶液中云母表面吸附后的演化过程。该界面受到能够影响单个离子和簇横向运动的剪切流作用。结果表明，当形成基团时，金属离子倾向于以相对较慢的动力学移动，这正如相关基团运动所预期的那样，对于给定原子位点上的单个离子，平均停留时间尺度约为1 - 2秒。簇的平均基团速度取决于离子的电荷密度，并且可以由离子的水合状态来解释。流体的横向剪切流不足以使离子解吸，但通过作用于靠近表面的离子间接影响扩散动力学。这些结果为剪切流下吸附在浸没固体上的离子簇动力学提供了见解。
